$2ln + 8m + 6n + 9 = 5m + 10n - 2$ Solve for $l$.
Combine constant terms on the right. $2ln + 8m + 6n + {9} = 5m + 10n - {2}$ $2ln + 8m + 6n = 5m + 10n - {11}$ Combine $n$ terms on the right. $2ln + 8m + {6n} = 5m + {10n} - 11$ $2ln + 8m = 5m + {4n} - 11$ Combine $m$ terms on the right. $2ln + {8m} = {5m} + 4n - 11$ $2ln = -{3m} + 4n - 11$ Isolate $l$ ${2}l{n} = -3m + 4n - 11$ $l = \dfrac{ -3m + 4n - 11 }{ {2n} }$